First obstacle with my "new" '99 ESC

So, I replaced the battery (which had gone dead from sitting) (so I'm told)) and now I have a "security system- vehicle may not re-start" message, and no fuel.

How do I go about re-setting the system so that the car knows it hasn't been stolen?

Sure, I could dig through Alldata, but I'd rather get it from you guys... much quicker and in language I can understand!